The present invention relates to a method and an apparatus for cleaning dies used for resin-sealing an article, and more particularly to a method and an apparatus for removing organic and inorganic residual substances from dies used for resin-sealing an article such as electronic devices such as electronic devices, for example, semiconductor devices.
The resin-sealing dies are used for resin-sealing semiconductor devices. A resin material used for resin sealing comprises a mixture of various organic and inorganic substances and also includes mold release agent such as wax for facilitating the molded resin product to be released from the dies. If the semiconductor device is sealed with the resin comprising the mixtures of various substances, then a chemical reaction or a polymerization reaction may be caused whereby those substances are deposited on surface of the resin. A part of the deposition on the resin may be adhered on internal surfaces of the dies. As a result, the deposition resides as dirt in hollow portions of internal surfaces of the dies.
Such residual dirty substances becomes accumulated and deposited to increase in size through repeated resin molding operations. The size-increased residual dirty substances changes a shape or a definition of the molded resin product from the predetermined shape or definition defined by the inner shape of the dies. Namely, the size-increased residual dirty substances form deformations or recessed portions in the molded resin product. Even if such the depositions of the residual dirty substances are uniformly adhered on the hollow portions of the dies, then the molded resin product is varied in thickness whereby a problem with a moisture resistance may be raised. To avoid those problems, it is necessary to carry out a periodic cleaning to the dies.
It is, however, important to conduct the required cleaning to the dies without providing substantive mechanical damages to the inner surfaces of the dies. For example, a cleaning solution is first applied on the inner surfaces of the dies for subsequent molding a resin such as a melamine resin having a relatively strong adhesive force with the dirty residual resin so that the deposited dirty residual resin is adhered with the molten resin and removed from the surfaces of the dies. Alternatively, a sheet type synthetic rubber having a strong adhesive force with the dirty residual resin is pressed onto the surfaces of the dies so that the deposited dirty residual resin is adhered with the sheet type synthetic rubber and removed from the surfaces of the dies.
The above conventional cleaning methods require time-consuming and inconvenient operations under high temperature and severe conditions. In order to settle this problem, it had been proposed to use a cleaning device so called as cleaner which is sandwiched between top and bottom dies during the resin molding process. This method is disclosed in Japanese laid-open patent publication No. 6-216175. FIG. 1 is a fragmentary cross sectional elevation view illustrative of a conventional cleaner inserted between top and bottom dies for cleaning the dies. A cleaner 19 is inserted between a top die 20a and a bottom die 20b. The cleaner 19 has top and bottom ozone supplying pipes 18 through which ozone is supplied to the top and bottom dies 20a and 20b to form a highly concentrated ozone atmosphere at about 10000 ppm in internal space of the dies 20a and 20b. The cleaner 19 also has top and bottom ultra-violet ray supplying pipes 17 for irradiating ultraviolet rays onto the ozone atmosphere to form a large amount of oxygen radical so that the dirty organic substances are decomposed by the oxidation and removed from the surfaces of the dies. The cleaner 19 also has top and bottom brushes 21 for cleaning the surfaces oft he top and bottom dies 20a and 20b.
The above conventional cleaning device has the following problems. Indeed, the organic dirty substrates are decomposed by the operations of the oxygen radicals formed by the ultraviolet ray irradiation onto the highly concentrated ozone atmosphere. Notwithstanding, inorganic residual substances could not be decomposed. The oxidation by the oxygen radicals may also remove a mold release agent applied on the surfaces of the top and bottom dies 20a and 20b. If the mold release agent applied on the hollow portion of the dies is removed or peeled by the oxidation, then the molten resin is unlikely to be released from the hollow portion, whereby the molten resin resides at the hollow portion of the dies. Such the residual resin on the hollow portion may cause defamation or form a recessed portion of the molded resin product.
Further, ozone and dusts in the dies may be dispersed to the outside of the dies or the atmosphere. This is harmful to the health of human. On the other hand, ozone in the highly concentrated ozone atmosphere in the dies may partially reside within the dies, whereby the residual ozone causes oxidation of metal of the dies, thereby forming rusts on the die surfaces. As a result, the life-time of the dies is remarkable shortened.
Furthermore, for cleaning the dies with the brushes 21, it is necessary to move the cleaner 19. This makes the mechanism of the cleaning system complicated.
In the above circumstances, it had been required to develop a novel method and an apparatus for cleaning dies free from the above problems.